This invention relates to phosphate coatings of metals and more particularly to microcrystalline zinc phosphate coating baths and processes for preparing and using the same.
It is well known in the metal finishing art to provide metal surfaces, particularly ferrous metal surfaces, with an inorganic phosphate coating by contacting the surface with an aqueous phosphating solution. The phosphate coating generally protects the metal surface against corrosion and serves as an excellent base for the subsequent application of organic coatings, such as paint, lacquer, varnish, primers, synthetic resins, elastomers, enamels, oils, drawing compounds, lubricants, and the like.
In the past, in order to obtain satisfactory coatings, it has been necessary to employ and maintain the coating baths at high temperatures, e.g., in the order of about 160.degree. F. to 200.degree. F. In doing so, large amounts of energy are consumed. Typical of coating baths which need to be employed at high temperatures are those disclosed, for example, in U.S. Pat. Nos. 3,090,709 and 3,676,224.
In view of the present high costs of energy and the need to conserve energy, it has become desirable to provide phosphate coating baths for metals which can be used at low temperatures, thereby reducing the amount of energy consumed in the process, but which still provide excellent corrosion resistant coatings and coatings which are excellent bases for subsequent painting, and the like.